My clownfish was behaving a bit differently today hiding behind the heater, I was worried as it was different so I tested the water, ammonia 0, ph 8.0, nitrite 0, nitrate 5. I did a partial water change to bring nitrates back down. After this they both swam around fine using the whole of the tank (they'd always stayed right at the top of the tank) so it was really nice to watch. On a few occasions one of them lay at the bottom on the rocks for a bit but then would move around fine again. The cleaner shrimp showed an interest and each time he got near the clownfish would fly off again, until one time when he stayed there and allowed the shrimp to clean him, it was fascinating to watch but then I realised he wasnt moving and then saw that my Mithrax crab had hold of him from under the rock he was lying next to. I can't work out if there was something wrong with him and was dying anyway or if the crab killed him. The remaining clownfish seems fine, I'm gutted and lost as to what to do next. I started the biube 4 months ago, it's a 35litre tank and I was really careful to cycle it properly and only added things at the right time, we now have 1 clownfish, 1 small cleaner shrimp, 1 small hermit crab, 1 Mithrax crab & 3 turbo snails. I'm sure I should have added more info but I can't think what else you might need to know, could really do with some advice on what happened and what to do next I'm feeling out of my depth.

Thanks Dave,
Should I be checking for anything else though? I've read about people checking for calcium. Frightened I'm missing something and the other clownfish will be affected. It will be easier if it was the crab as I can't imagine there's much chance that would happen again. Also how do I get another clownfish? The smaller one has died so I'm left with the female? Is that right?

Wasn't the crab, my other clownfish died last night. I can't work out what's wrong. I've tested the water again today with API kit and everything is fine. Ph is bit low 7.8 but from what I've read this shouldn't be a problem? PH has always been around 8, could it be that it wasn't high enough and I need to look at calcium? I was only told I needed to check ammonia, ph nitrite and nitrate, salinity and temp. What am I missing?!

Did you do any house projects...like paint, or was there any pet sprays, air fresheners, etc? We lost a pair of clowns years ago after painting a wall in anotrher room with latex paint. Dr. Mac @ Pacific East Aquaculture pinned that as the reason for deaths.

It's a biube tank which is 35l, I've used the cured live rock that came in the marine conversion kit plus the ceramic media. It's been running since September, after 2 weeks I added 3 hermit crabs, after 8 weeks all levels were perfect so I got the clownfish which were a tank bred pair. Since added a small cleaner shrimp & some snails as previous snails had been eaten by hermit. The water levels have always been good but nitrates never seem to be at 0. Normally about 5 but have been as high as 40. I do a 20% water change every week to try to fix this. Nitrite always 0 though & it's never seemed to bother them except that they stay high up in the tank most of the time. I have no plants in my tank as I was nervous on how to do this, could that be a problem. Also I only feed hikari marine s pellets as I found mussel was ruining the water. The fish would only take what's at the top & never went down to the bottom for what was left. I feel like I'm doing it all wrong after just getting in to the swing of things. Could it be the nitrates have just been an ongoing strain on them? & how do you sort them in the tank?

The nitrates should Not have been the issue. There has to be something else going on. Any chance of outside contaminates getting into the tank like Dave mentioned. So you buy premixed saltwater from LFS. Have you ever checked that?

Sorry forgot to answer that, nope no painting or any air fresheners etc. can't think of any pollutants whatsoever there's been no change in the house. No I've never thought to check the water from lfs which is frustrating as I've used the last bit yesterday on a water change. The shrimp, crabs & snails are all doing fine I'm so confused. When I do the water change I try to get any dirt from the media out could I be cleaning it too much & removing the bacteria needed?

If this was the case, you would have seen a spike in ammonium. Most likely your liverock is doing most of the filtering for you anyway. It is just strange since, inverts are usually more sensitive to water quality than fish.

Nope never anything but 0 on ammonia. Just the nitrates that I have problems with at times. It's so confusing, I suppose I'll have to watch the other guys in the tank for a bit & see what happens. I'm too frightened to put any fish in without knowing what could be wrong.
Thanks for the replies I really appreciate it.

I just dealt with a similar situation in my JBJ 12 nano. I lost a spot tail blenny (one of my favorites) and a blue spotted jawfish (ouch!) and a firefish goby all in a 2 week span.

It all started with the jawfish. I saw his tail had some serious trauma to it but at first I thought a rock had fallen on it or something. Found him the next morning. Blenny was next but I never saw anything suspicious with him. Just found him onee morning. All of my water has checked out fine.

And my porcelain crab is the only one I can see being responsible for it as I found him picking at the firefish as the last victim on the sandbed one morning. He's been acting totally different as well (hard to explain).

Wow, s'pose I should be glad I only had the 2 fish to lose. That must be devastating. I'm sure my crab didn't kill my fish especially as I watches the 2nd one die. Crab only came out when the fish was laying on the bottom.
What will you do?

i had a pair of black clowns in my 10 gallon nano had a similar situation. they both died the same day. the crabs and snails and even anemones survived and are still alive. i have since put a fire fish and bicolor blenny in and they have been doing fine. maybe just a bad batch of clowns. thats what i think mine was.